Proposals have been made for a time-division driving in which one frame is divided into a plurality of sub-frames (for example, a first sub-frame and a second sub-frame) and an input gray scale is displayed as a result of a summation of respective display of the sub-frames (for example, see Patent Document 1).
FIG. 7 is a graph for determining a gray scale of the first sub-frame and a gray scale of the second sub-frame, for each input gray scale. According to the graph shown in FIG. 7, the gray scale of the first sub-frame is set not more than the gray scale of the second sub-frame for each of the input gray scales. This allows the first sub-frame to be a dark sub-frame (a sub-frame having low brightness) and the second sub-frame to be a bright sub-frame (a sub-frame having high brightness). For example, when an input gray scale is 192 gray scale, the first and second sub-frames are set to have 56 gray scale and 249 gray scale, respectively. When an input gray scale is 64 gray scale, the first and second sub-frames are set to have 4 gray scale and 159 gray scale, respectively. As a result of a summation of respective display of the sub-frames, an input gray scale (192 gray scale or 64 gray scale) is displayed.
FIG. 8 illustrates one example of a moving image displayed based on such a time-division driving. FIG. 8 illustrates an image P moving to the right in a black background. In the image P, an area X which has 192 gray scale and an area Y which has 64 gray scale are adjacent to each other, i.e., a high gray scale area X and a low gray scale area Y are adjacent to each other so that their respective adjacent edges form a line.
In this moving image display, the first and second sub-frames are set to have 56 gray scale and 249 gray scale, respectively, in the area X. In the area Y, the first and second sub-frames are set to have 4 gray scale and 159 gray scale, respectively. sFa through sFf shown in FIG. 9 schematically illustrates display for each sub-frame in this moving image display.
More specifically, a right edge of each of the areas (X, Y) in the image P is of a rising response from 0 gray scale. The first sub-frame of the area X has a visible 56 gray scale, whereas the first sub-frame of the area Y has an invisible 4 gray scale. The second sub-frame of the area X has a visible 249 gray scale, and the second sub-frame of the area Y has also a visible 159 gray scale.
[Patent Document 1]
Japanese Unexamined Patent Publication, Tokukai, No. 2005-173573 (published Jun. 30, 2005)